Tandem drive axle assemblies having a forward rear axle and a rearward rear axle in proximity with each other are well known. Such tandem drive assemblies are widely used on heavy duty trucks and other over-the-road vehicles, such as busses, which have a high vehicle weight and/or a high load carrying capacity. In such assemblies, both rear axles may be power driven.
An inter-axle differential (IAD) is commonly employed in such vehicles to split the input shaft torque between the front and rear axle of the tandem drive axle assemblies. It is common for an operator of such vehicles to engage and disengage a lock out that overrides or disables the IAD through the use of a pneumatic switch, which typically is mounted on the vehicle dash. In turn, the pneumatic switch applies air to an axle mounted actuator, which engages a sliding dog clutch to “lock” the inter-axle differential.
However, there are several shortcomings to the above-described manual methods of engaging/disengaging the IAD. Failure of the vehicle operator to notice wheel end slip occurring and engage the IAD, can result in spin out failures. Also, engagement of the IAD, while significant slipping is in process, can result in damage to the drive axle. Leaving the IAD engaged for an extended length of time can result in “drive line wind-up” and a resulting inability to disengage the IAD without reversing the vehicle. As a result of these shortcomings, extended wear can occur and the operator may not notice the wear, as actual engagement and disengagement of the IAD is not typically indicated.
Recently, automatic inter-axle differential lockout mechanisms have come into use, where typically two speed sensors (i.e., associated with an IAD clutch locking gear and an IAD helical gear) have been employed to monitor IAD gear speed (see, for example, U.S. Patent Application Publication No. 2006/0154787 to Claussen et al., which is incorporated herein). For such an IAD lockout mechanism to function properly, the mechanism must separately identify each speed sensor. Hence, it is common to specifically wire between the speed sensors and a control unit by way of different harness connectors, plugs, keys, etc., and to specifically install different sensors so that the sensors cannot be wired the same and/or communicated with through the same signals to the control unit. It is also common that for calibrating each of the gears used in the IAD, the correct combination of the number of teeth for each gear needs to be determined manually and in advance of utilization of the gears, in order to correctly calculate revolutions per minute (RPM) of the gears being monitored.
Examples of relevant art involving inter-axle differential lockout mechanisms are as follows. U.S. Pat. No. 5,927,422 to Schakel generally discloses a system for correcting drive wheel slippage in a heavy vehicle. A central processor compares the driveshaft speed to a non-driven wheel speed and locks an inter-axle differential of a tandem rear drive axle to drive front and rear drive axles at the same speed. If necessary, the inter-axle differential may alternatively lock a main differential of a single rear drive axle to drive first and second driven wheels at the same speed when the ratio of the driveshaft speed signal to a first non-driven wheel speed signal exceeds a predetermined limit. In a tandem configuration, if drive wheel slippage continues, main differentials of the front and rear drive axles are also locked.
U.S. Patent Application Publication No. 2006/0036361 to Romer teaches a drivetrain protection and management system that monitors and determines individual wheel speeds to detect wheel spin and slip conditions on a drive axle. When wheel spin or slip exceeds a threshold, the system automatically controls input torque to the drive axle by controlling engine or retarder torque. In addition to monitoring wheel speeds, the system monitors other vehicle characteristics such as engine torque/speed, the transmission ratio speed, transmission output speed, vehicle speed, and throttle position.
U.S. Patent Application Publication No. 2006/0175113 to Rodeghiero teaches a vehicle that includes steerable front wheels and an interaxle differential for transmitting torque from an engine to the front wheels and to rear wheels. The differential includes a controllable clutch operable to control a ratio of front wheel speed to rear wheel speed, while a control unit controls the clutch as a function of sensed steering angles and stored information including steering angles and corresponding front to rear wheel speed ratio values. The control unit, which is automatically calibrated, periodically obtains steering angle values and front and rear wheel speed values, it generates new front to rear wheel speed ratio values, and replaces one of the stored front to rear wheel speed ratio values with one of the new ratio values, if the steering angle values indicate that the vehicle has been in a straight ahead travel mode for at least a certain time period.
In contrast to the above cited relevant art, the present invention seeks to automatically determine the configuration (e.g., location of the IAD clutch locking gear and the IAD helical gear) of the IAD sensors and to automatically determine the correct combination of the number of teeth in each of the IAD gears so that each of the IAD sensors can be automatically calibrated. The present invention further seeks to not require the exact wires between the ECU sensor inputs and the IAD sensor terminals to be connected to each other, thus precluding the possibility of the sensors being installed at the wrong locations. As a result, the present invention seeks to reduce installation and maintenance complexity, along with reducing costs by not requiring separate connectors, identification, and sensors.